Paula Goodyer

There was a time when gastroenterologist Professor Katie Allen dismissed food allergy as something that had been overhyped by the media – until two things changed her mind. One was going to work in a hospital allergy unit and seeing first-hand how common the problem was. The other was taking a bite of toast with peanut butter and feeling her throat start to swell until it felt like she'd swallowed a small golf ball.

Now she's a senior researcher into food allergy at Melbourne's Murdoch Childrens Research Institute and – just in case – she carries an EpiPen, the injection kit that provides first aid for anaphylaxis, a life-threatening allergic reaction.

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Two generations ago, EpiPens were unheard of and taking peanut butter to school didn't provoke hostile debate between parents. Back then allergies were uncommon, especially food allergy. Now around one in 50 Australian children has a peanut allergy. A 2013 study by a team of researchers led by Katie Allen found that one in 10 children aged 12 months living in Melbourne had a food allergy – the highest incidence of food allergy ever reported in the world. Hospital admissions in Australia for severe allergic reactions for anaphylaxis due to food allergy in children aged four and under have jumped five-fold in the past 10 years.

We live in an age of food panic – carb panic, sugar panic and, more recently, berries-from-China panic – so it's easy to think that with food allergy the enemy is food, especially foods such as cow's milk, peanuts, tree nuts, seafood, sesame, soy, fish and wheat that are most likely to trigger allergy.

But the problem isn't food – instead there's a growing recognition among scientists that something is sabotaging our immune systems.

Senior allergy researcher Professor Katie Allen. Photo: Emma Phillips

The suspect is a mix of changes to how we live that has occurred relatively rapidly, and may include cleaner environments, too much over-processed food, insufficient vitamin D – and, possibly, our expanding waistlines, says Professor Susan Prescott in a new book, Origins, an early life solution to the modern health crisis. In it, Prescott, from the School of Paediatrics and Child Healthat the University of Western Australia, looks at what it might be about Western lifestyles that can mess with our immunity and leave us vulnerable, not just to allergy, but to common autoimmune diseases such as coeliac disease (where the digestive system reacts adversely to gluten) and Type 1 diabetes.

Let's start with the gut. Not just a place for digesting dinner, it houses millions of microbes that can influence our health, including the immune system. Research suggests that the kind of microbes inhabiting the gut in early childhood may affect how well a fledgling immune system develops, says Prescott. But there are signs that modern lifestyles have altered our gut microbes and that this is affecting our immune system. Although it's not clear what the ideal mixture of microbes is and how to attract them, there are clues. One is that what you eat helps determine which microbes live in your gut. One example is fibre, which works as a prebiotic. This means it provides food for friendly microbes, helping good bacteria to flourish. But with so much highly processed food, Western diets can be light on fibre. However, research in young children has found that giving prebiotic supplements has a beneficial effect on the microbes in the gut, says Prescott. It also reduces eczema – and children with eczema are more likely to develop food allergy.

The microbes we meet outside the gut may make a difference too – it could be that exposure to a broader range of microbes in early childhood may help to stimulate the immune system.

"There's evidence that mothers who live in high microbial environments during pregnancy are less likely to have allergic children," says Prescott, pointing to families in Bavarian farmhouses where the human dwelling shares the same building as the barn and cattle stalls. "Children growing up in this space have much less allergy, hay fever and asthma."

"We know that people born in Asia have a lower risk of developing food allergy yet when they migrate to Australia and have children here, these children have three times the risk of Australian children," Katie Allen says. "We think that in Asia there are some protective factors –possibly because in Asia the food supply is different and people are exposed to more infections and that these things help to kick-start the immune system in early childhood."

Prescott also believes there could be a connection between the rise in food allergy and the rise in obesity. More research is needed – but childhood obesity increases the risk of asthma and food allergy, according to some studies, and there's emerging evidence that children of overweight mothers have an increased asthma risk.

Although food allergy is common in childhood, there's a good chance of outgrowing it, especially allergies to eggs, milk, soy and wheat. The food allergies most likely to stick around for life are allergies to peanuts, tree nuts, seeds and seafood. Around one in 50 adults in Australia has a food allergy and although most developed it as a child, some – like Katie Allen – developed theirs as an adult.

"One theory is that it occurs when you're exposed to a food later in life that you've never been exposed to before – another is that something 'resets' the immune system. In my case I'd become pregnant and in pregnancy there are changes to the immune system to prevent the body from rejecting the baby," she says. "But I'd also moved to the US and I was exposed to different foods and different microbes and possible different levels of vitamin D which might have been factors," Allen says.

With no cure for food allergy, the only way to manage it is to stay away from the problem food, keep the EpiPen close – and hope that people who offer you food take your problem seriously.

"I've experienced some eye rolling in the past – and someone who served me chopped nuts on ice-cream – and I find myself apologising a lot," Allen says. "But I think people are becoming more understanding and also more open to asking others if they have any particular food needs. I think it's up to all of us to make others feel comfortable about declaring if they need to avoid certain foods."

What if you suspect a food allergy?

It's tempting to trawl the internet to self-diagnose a food allergy or other food sensitivity, but a smarter option is to see a doctor, who can refer you to a specialist allergist or hospital allergy clinic.

For more information, see the Australasian Society for Clinical Immunology and Allergy, allergy.org.au